Rach Quasi-Colocation Association

1. A method of wireless communication of a user equipment (UE), comprising: receiving a first Demodulation Reference Signal (DMRS) on a serving control channel of the UE; determining that a random access event has occurred; receiving a plurality of down-link reference signals each being a Synchronization Signal Block (SSB) or a channel state information reference signal (CSI-RS); selecting a first down-link reference signal from the plurality of down-link reference signals, the first down-link reference signal being quasi-colocated with the first DMRS and UE-specifically configured or predefined; selecting a first message from a group of messages that each are associated with the first down-link reference signal; and sending the first message to a base station to request a random access to the base station.

2. The method of claim 1 , wherein the first message includes a preamble sequence, wherein the first message is selected from a group of messages that are associated with the first down-link reference signal.

3. The method of claim 1 , wherein the first down-link reference signal is a synchronization signal block.

4. The method of claim 1 , wherein the first down-link reference signal is directly quasi-colocated with the first DMRS.

5. The method of claim 1 , wherein the first down-link reference signal is quasi-colocated with the first DMRS through one or more intermediate signals.

6. The method of claim 1 , wherein, when the UE is in a connected state, the random access event includes at least one of: reception of a request from the base station to initiate a random access to the base station; a handover of the UE from a second base station to the base station; an up-link data arrival without up-link synchronization; a down-link data arrival without up-link synchronization; and a beam failure recovery request.

7. The method of claim 6 , further comprising: receiving a second message from the base station in response to the first message by assuming that a DMRS included in the request and a DMRS included in the second message are quasi-colocated.

8. The method of claim 7 , wherein the random access event is the reception of the request, wherein the request is a physical downlink control channel (PDCCH) order, wherein the second message includes a PDCCH command and a random access response.

9. The method of claim 7 , wherein the random access event is the beam failure recovery request, wherein the second message is scrambled by a cell radio network temporary identifier (C-RNTI) of the UE.

10. An apparatus for wireless communication, the apparatus being a user equipment (UE), comprising: a memory; and at least one processor coupled to the memory and configured to: receive a first Demodulation Reference Signal (DMRS) on a serving control channel of the UE; determine that a random access event has occurred; receive a plurality of down-link reference signals each being a Synchronization Signal Block (SSB) or a channel state information reference signal (CSI-RS); select a first down-link reference signal from the plurality of down-link reference signals, the first down-link reference signal being quasi-colocated with the first DMRS and UE-specifically configured or predefined; select a first message from a group of messages that each are associated with the first down-link reference signal; and send the first message to a base station to request a random access to the base station.

11. The apparatus of claim 10 , wherein the first message includes a preamble sequence, wherein the first message is selected from a group of messages that are associated with the first down-link reference signal.

12. The apparatus of claim 10 , wherein the first down-link reference signal is a synchronization signal block.

13. The apparatus of claim 10 , wherein the first down-link reference signal is directly quasi-colocated with the first DMRS.

14. The apparatus of claim 10 , wherein the first down-link reference signal is quasi-colocated with the first DMRS through one or more intermediate signals.

15. The apparatus of claim 10 , wherein, when the UE is in a connected state, the random access event includes at least one of: reception of a request from the base station to initiate a random access to the base station; a handover of the UE from a second base station to the base station; an up-link data arrival without up-link synchronization; a down-link data arrival without up-link synchronization; and a beam failure recovery request.

16. The apparatus of claim 15 , wherein the at least one processor is further configured to: receive a second message from the base station in response to the first message by assuming that a DMRS included in the request and a DMRS included in the second message are quasi-colocated.

17. The apparatus of claim 16 , wherein the random access event is the reception of the request, wherein the request is a physical downlink control channel (PDCCH) order, wherein the second message includes a PDCCH command and a random access response.

18. The apparatus of claim 16 , wherein the random access event is the beam failure recovery request, wherein the second message is scrambled by a cell radio network temporary identifier (C-RNTI) of the UE.

19. A non-transitory computer-readable medium storing computer executable code for wireless communication of wireless equipment, comprising code to: receive a first Demodulation Reference Signal (DMRS) on a serving control channel of the UE; determine that a random access event has occurred; receive a plurality of down-link reference signals each being a Synchronization Signal Block (SSB) or a channel state information reference signal (CSI-RS); select a first down-link reference signal from the plurality of down-link reference signals, the first down-link reference signal being quasi-colocated with the first DMRS and UE-specifically configured or predefined; select a first message from a group of messages that each are associated with the first down-link reference signal; and send the first message to a base station to request a random access to the base station.

20. The non-transitory computer-readable medium of claim 19 , wherein the first message includes a preamble sequence, wherein the first message is selected from a group of messages that are associated with the first down-link reference signal.